Pheumocystis carinii pneumonia is the most common opportunistic injection due to AIDS. Current therapy is inadequate. Trimetrexate has been proposed as experimental therapy because it is highly lipophilic and is taken up and concentrated in protozoan cells. This agent is being administered togehter with leucovorin calcium in an effort to attain therapeutic effects with less toxicity. Specifically it is anticipated that mucositis and bone marrow toxicity may be prevented.